This invention relates to an electron beam exposure apparatus of raster scan type for line scanning an exposure medium, such as a semiconductor wafer or a mask, with an electron beam of small amplitude while the medium is moved in a direction perpendicular to the line scan direction so as to draw a pattern on the medium.
The electron beam exposure apparatus of raster scan type usually has a construction as shown in FIG. 1. The apparatus includes a control computer which effects input and output processing of various data and controls the apparatus. Data corresponding to a pattern to be drawn is fed from a magnetic tape device 2 to the computer 1. The input data is converted into data suited for a function generator to be described later and then stored in a magnetic disk device 3. The stored data is transferred from the computer 1 to the electron beam exposure apparatus 4 when drawing the pattern. The exposure apparatus 4 includes an operation panel 5, a control interface 6 coupled to the operation panel 5, and a deflector 7 for deflecting an electron beam. The apparatus 4 further includes a stage 9, on which a medium 8, for instance a mask, on which to draw a pattern, is placed. The stage 9 is operated by a motor 10. The apparatus further includes an electron gun 11 for generating an electron beam 12. Along the path of the electron beam 12 from the electron gun 11, an electrostatic deflecting plate 13 for electrostatically deflecting the electron beam 12 and an electron lens 14 are provided. The electron lens 14 and electron gun 11 are furnished with power from a power source circuit 15. The component parts mentioned above are supported on a quake-proof base 16.
In the operation of the electron beam exposure apparatus to draw a pattern on the mask 8, the electron beam 12 from the electron gun 11 is deflected by the electrostatic deflecting plate 13 to scan the mask with a constant amplitude, as shown at A in FIG. 2. Concurrently, the stage 9 is continuously moved by the motor 10 at a constant speed in a direction Y perpendicular to the direction X of scanning by the electron beam 12. Thus, a rectangular region 8a of the mask 8 having a constant width A is scanned. When the region 8a is entirely scanned from the upper end to the lower end of the mask 8, the stage 9 is displaced sidewise, i.e., in the direction X, by the same amount as the electron beam scan amplitude A. The next rectangular region 8b adjacent to the first one 8a is now scanned from the lower end to the upper end. In this way, successive rectangular regions are progressively scanned to cover the entire surface of the mask 8. While the mask 8 is being scanned in the above manner, pattern data stored in the magnetic disk device 3 is transferred through the control computer 1 to the control interface 6 and stored in a buffer memory, not shown, provided in the control interface 6. The stored data is converted by a function generator into dot pattern data. The dot pattern data thus obtained is stored in a dot pattern memory and read out therefrom to be used for blanking (ON/OFF) control of the electron beam 12. In the above way, a pattern corresponding to the pattern data stored in the buffer memory in the control interface 6 is formed on the mask 8 according to the scanning of the mask 8 by the electron beam 12.
With this apparatus, the dot pattern data produced from the function generator may contain protrusion patterns or space patterns as typically shown in FIGS. 3A and 3B, which result from errors generated in quantization in the dot pattern conversion or errors generated in data conversion process in the computer 1 prior to the quantization process. In another aspect, it is thought that when the electron beam 12 strikes the exposure medium i.e. the wafer or mask, charge is developed and stored around the point of incidence of beam according to the Gaussian curve. This is thought to take place even if the beam diameter is infinitesimally reduced. Therefore, in a case where two patterns are located in the close proximity to each other, these patterns are liable to be distorted due to a proximity effect as shown in FIG. 3C. This results from an overlapping effect of the charge that is stored in the manner as described above on areas which are not directly impinged upon by the electron beam (these areas becoming etchable in case of a positive photoresist). Further, for correcting (either increasing or reducing) pattern dimensions, the relevant data is converted by the computer 1 into data suitable for the function generator or appropriately processed when they are read out from the magnetic tape device 2 before being supplied to the function generator. Therefore, an extended process period is required for the computer processing to reduce the system efficiency.